July babies

Shopping for clothes for my baby girl coming early july. Being in Arizona, summer isn't so light here. Not sure of how much summer clothes I should buy? As far as newborn-3 months or 0-3 months. Not even sure if i'm making sense, but I know some babies don't fit in the newborn clothes long or some are in 3 months clothes early. Can any moms give me some advice on what I should get? Doesn't really get cold here until late October, almost Nov.